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UltravioletPhotography

Are longpass filters useful for transmission testing?


rfcurry

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Yes, Jonathan, I think it would be very useful to have similar graphs for the Baader U and LaLa U. We are discussing the general concept of the precision of the longpass filters and the Sparticle filters in identifying discrete wavelengths of transmission, not just the potential and actual transmission of one UV bandpass filter. So, please, give us more! :)

 

Thanks.

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Andrea, the effect I mentioned about sunlight and camera sensitivity changing will for sure be small, and I'm not even sure over that range of wavelengths whether it would have any effect. But I wanted to mention them for completeness.

 

EDIT - I have deleted my spectra, to avoid confusion.

 

 

Now for the Sparticle images. These were taken on my multispectral EOS 5DSR, with 105mm Rayfact lens, ISO400, f5.6, 2s exposure, with the Sparticle aimed at a blue sky, away from the sun. Taken as RAW files, and opened in Raw Digger as RAW composite files. Screen grabbed and cropped. The 404nm filter is on the bottom row, in the middle. The 405nm filter is on the bottom row on the right hand side.

 

SEU II Sparticle image

post-148-0-28260600-1541257373.jpg

 

Baader U Sparticle image

post-148-0-98255300-1541257369.jpg

 

La La U Sparticle image

post-148-0-21553600-1541257371.jpg

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Jonathan,

 

I just noticed that the SEU Gen2 data you used in your two recent posts was far different than the data Ulf gathered. Looking at 400nm, the SEU Gen2 on your graph is approx. 40%; Ulf has 24.1%. Looking at the 404 filter, at approx. 40% at 400nm, the Light-to-lens (product of SEU Gen2 and 404nm filter) is shown as 16%, whereas, it should be 9.6% by Ulf's measurement. That is a big difference. The result is that the potential transmission of the SEU Gen2 by 404nm filter curve appears much greater in amplitude than it would be in fact.

 

Do you have Ulf's data on the SEU Gen2?

I hope you can correct that, as it is significant.

 

Thanks.

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As mentioned before Reed (a few posts ago) my system has not been re calibrated since buying it, so I'm not hugely surprised there is a difference to Ulfs. I was very clear in pointing that out. I have a calibration light source on order but it won't be with me until the end if the month. If you would prefer I can delete the post, the last thing I want to do is add confusing data again.

 

What I would say though is the Sparticle is at least trending how I would expect it too, based on the transmission data for the different filters.

 

EDIT - Based on the concerns over the spectra I am deleting the spectra from my post comparing with the Sparticle images in this thread, to avoid potential confusion I'll leave the Sparticle images up though, as they are independent of any spectrometer calibration. I will revisit any filter transmission measurements, once my new calibration setup has arrived, although I would need to destroy my Sparticle to get the filters out, unfortunately, as they were glued in when making it.

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Hi Jonathan,

 

I think we are always going to have problems when, as a forum, we can't agree on data sources. At 400nm, your SEU Gen2 is 166% greater than Ulf's; whereas, at 400nm, your Baader U is 58% of Ulf's.

 

What this means is that your data is spreading the difference between the SEU Gen2 and the Baader U unrealistically. Ulf's data shows a ratio of 23.4:1, SEU Gen2 to Baader U at 400nm. Your data spreads that to 65.1:1, SEU Gen2 to Baader U at 400nm. That vast difference clashes with the evidence of the Sparticle itself.

 

Your recent Sparticle images should illustrate the differing transmissions of the filters. However, if we look at them, they do not show the spread that the graphs indicate. The GS images below were rendered grayscale by brightness.

 

Baader U (400px wide) Baader U (grayscale 400px wide)

http://uvroptics.com/images/Baader%20Sparticle2%20400px.jpg http://uvroptics.com/images/Baader%20Sparticle2%20Grayscale%20400px.jpg

 

SEU Gen2 (400px wide) SEU Gen2 (grayscale and 400px wide

http://uvroptics.com/images/SEU%20Sparticle2%20400px.jpg http://uvroptics.com/images/SEU%20Sparticle2%20Grayscale%20400px.jpg

 

The 405nm Sparticle in grayscale is 10 of 256 for the Baader U and 97 of 256 for the SEU Gen2. Change to percentages and the ratio of SEU Gen2 transmission to Baader U transmission is 12.7:1. Your graphs would indicate a ratio of 65.1:1... 5.13 times greater than the Sparticle images show.

 

It looks like the problem is greater than your spectrometer calibration.

 

I do appreciate your work. Thanks.

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What is the formula for getting "brightness" from the color images, Reed? Several members have attempted to derive the Sparticle colors from the spectra graphs (with different data sets) and nobody has managed to get it right in that direction. It seems really iffy to me to attempt it in the other direction also. The spectroscopy data may indeed need calibration, but calling in question everything Jonathan has done seems a little much?
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The filters have been measured at different times on different days, so I can understand that drift has occurred, even simply as a result of that. As the values around 400nm are already very low, very small changes in wavelength will have a big percentage difference when looking at the values.

 

At least the camera images of the Sparticle aren't subjected to spectrometer drift. What they do emphasize though is the effect of sensitivity drop and light intensity drop as a function of wavelength. On your greyscale images above, the 404nm and 405nm Sparticle filters (bottom middle and right) are darker than the rest of the Sparticle filters other than the top left and top middle ones (303nm and 321nm respectively) on the Baader U image. By eye, as I'm not measuring it, the SEU II greyscale images, the 404nm and 405nm Sparticle filters look to be somewhere around the same brightness as the middle Sparticle filter which is the 364nm one.

 

But (and it is a big but) even this is an over simplification. It is all further complicated by the Sparticle filters not all transmitting the same amount - the 404nm and 405nm ones transmit much more than one at 382nm and below, over emphasizing potential issues. Just goes to show how many variables there are when looking at these things, and how some things can over emphasize results. I prefer to use the Sparticle for relative tests, not absolute ones - change one variable at a time and see the effect.

 

I'm not sure to read this comment, "It looks like the problem is greater than your spectrometer calibration.", Reed. Perhaps I'm missing the context, but I'm not clear on that, but it is definitely a complex area.

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Jonathan,

 

I just noticed that the SEU Gen2 data you used in your two recent posts was far different than the data Ulf gathered. Looking at 400nm, the SEU Gen2 on your graph is approx. 40%; Ulf has 24.1%. Looking at the 404 filter, at approx. 40% at 400nm, the Light-to-lens (product of SEU Gen2 and 404nm filter) is shown as 16%, whereas, it should be 9.6% by Ulf's measurement. That is a big difference. The result is that the potential transmission of the SEU Gen2 by 404nm filter curve appears much greater in amplitude than it would be in fact.

 

Do you have Ulf's data on the SEU Gen2?

I hope you can correct that, as it is significant.

 

Thanks.

 

The SEU2 has a beautifully steep transition close to 400nm.

Even a small deviation in calibration will give big shifts in transition value at 400nm.

My original measurement was ca 0.7nm off at that wavelength giving a transition value of ca 24%.

When the wavelengths scale was calibrated the second measurement that I posted in this thread gave ca 32% at 400nm.

 

If Jonathan's currently uncalibrated spectrometer is off slightly more than 1nm in opposite direction, compared to my first measurement that would produce a transmission of ca 40%, assuming that the two filters we measured are completely identical.

A drift of around 1nm after more than a year is not impossible.

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Jonathan,

 

When I wrote "It looks like the problem is greater than your spectrometer calibration" I was referring to the divergence in your data from that of Ulf's. If the problem was only calibration, it would seem that your transmission curves for both the SEU Gen2 and the Baader U would be parallel (roughly) to Ulf's. However, as there was not parallelism but divergence, then one or both of you have problems other than calibration. Does that make any sense?

 

I'll measure the 400nm of the SEU Gen2 on my Hitachi U-1500 and get back to you. :) I still haven't gotten my diode array working. Hey, it's only been a year. :(

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Andy,

You asked "What is the formula for getting "brightness" from the color images, Reed? " Back in the day, I wrote graphics and imaging SW for a SW company. Great fun! We had a lot of different algorithms we wrote for filtering bitmaps. Here is a link to three simple algorithms for color to grayscale conversion - https://www.johndcook.com/blog/2009/08/24/algorithms-convert-color-grayscale/

 

I used luminosity.

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I don’t understand how you can say he is doing his spectra incorrectly for reasons beyond calibration and not be questioning all the prior work? It did seem kind of harsh, but I don't understand how else to reconcile things?
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In my humble opinion, this topic is not really about longpass filters, or bandpass filters, or spectrometers, or how to use them, or who has the best one,

but instead, the original intention of this topic seems to be centered on dispelling any idea that the SEU is not a 'UV-only' filter.

I leave it to others to define what a 'UV-only' filter is, should be, or what you want it to be.

Instead I will present a graph overlay, using Jonathan's spectrometer graphs of the SEU, and several stack plots using the Schott program.

First let me say to Jonathan, I hope it is OK to use your graphs in this overlay, please let me know if it isn't and I will gladly remove this post, this graph, or put your name on it, however you like.

Here are Jonathan's original graphs he made using his spectrometer. I used his top graph in this overlay graph below.

http://www.ultraviol...dpost__p__22664

 

I believe Jonathan used a Perkin Elmer Lambda 650S UV-Vis spectrometer for his graphs:

https://www.google.c...wiz.75JIgqrjt1o

 

Also, note: This is a combination of what I assume is a T graph (made by Jonathan) and Ti graphs made with the Schott program.

Because Jonathan's graph is linear, I didn't have any way to make a combined (stacked) T graph that was in linear form with the program.

Therefore the peak amplitudes of the two calculated stacks would be slightly lower in T form than they are presented as in Ti form on the graph below,

and the 400nm cross over points might be slightly lower also, again, if those graphs were presented in T form.

 

OK, so this graph compares the SEU with a U-360 1mm stack that is intentionally designed to be UV+VV (visual-violet),

and also with Ulf's UG2A stack, which is a UG2A 2mm + S8612 2mm stack, and it is also designed to be UV+VV, with even more VV content.

 

By the way, we all have Ulf to thank for the UG2A, because he asked for it, and pushed for it, and the UG2A is a welcome and useful addition to our repertoire of filters,

so that is why I have labeled his stack the "ULF U" on the graph below. :)

He has posted results using that stack several places on this board.

http://www.ultraviol...__fromsearch__1

 

http://www.ultraviol...__fromsearch__1

 

My handy dandy UV and Violet reference list:

UVA = 320nm to 400nm

Violet = 380nm to 450nm

VV = Visual Violet = 400nm to 450nm

UVAV or UVV = UVA Violet or UV Violet = 380nm to 400nm

 

Regardless of whether or not the SEU crossed the 400nm threshold at 45%, 24%, or 20%, I consider ALL of these filters/stacks to be UV+VV filters.

Please note how all of these filters on the graph below clearly transmit across the UV-only 400nm separation line, and have one foot solidly planted in VV.

There is nothing wrong with using any of these filters, and there is nothing wrong with UV+VV,

however, to define or classify any of these filters as being UV-only would be erroneous.

post-87-0-10369700-1541302341.jpg

 

This version may be a little easier to read:

post-87-0-46021200-1541306051.jpg

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I believe Jonathan used a Perkin Elmer Lambda 650S UV-Vis spectrometer for his graphs:

https://www.google.c...wiz.75JIgqrjt1o

 

I think that is not correct.

He has been using a Ocean Optics FX-spectrometer for quite some time now.

It is either a OCEAN-FX-UV-VIS or a OCEAN-FX-UV-VIS-ES.

https://oceanoptics....oduct/ocean-fx/

That is the one he and I have discussed how to calibrate with a reference lamp for some time now.

 

I'm shure Jonathan will let us know what he used.

 

I see that you honor me by your naming of one of my favourite UV-stacks. Thank you very much, Steve. :)

 

My handy dandy UV and Violet reference list:

UVA = 320nm to 400nm

Violet = 380nm to 450nm

VV = Visual Violet = 400nm to 450nm

UVAV or UVV = UVA Violet or UV Violet = 380nm to 400nm

 

The list here is an excellent idea! I like it very much.

I like to have clear definitions and that give a good common understanding when discussing things.

 

I have no opinion against the chosen names. They work well for me.

Another one might be UV-VIS border (400nm)

 

Together with that there should be some definitions of common decision levels to use for defining wavelength widths and cutoff wavelengths

Normally 50% of full transmission for cut on, cut off and FWHM.

https://www.google.c...haracteristics.

 

With the commonly used 50% decision level, by definition all filters we have discussed above will with margin fall into the UV-pass category.

There might be some real reason to use a different definition of decision level in this case, but I cannot see any.

 

For analytical purposes the amount of light passed from the VIS or NIR might be too big.

That varies from case to case, but do not change the fact that by normal definitions they are UV pass filters.

 

To define what would be a UV-only filter, one must decide what "only" means in OD terms both directly at the UV-VIS border and further into the VIS-NIR area.

 

I think the OD close by 400nm is application-dependent and would preferably be based on practical effects for a "normally" intended usage.

This would be a very interesting subject to discuss, maybe in a new thread.

 

A more important factor, for our type of photography might be some kind of measure of the total amount of transmitted light beyond 400nm.

I would then suggest some kind of weighting-factor dependent on how far away the light's wavelength is from 400nm.

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Thanks for explaining about the, "It looks like the problem is greater than your spectrometer calibration" comment Reed, yes that makes sense.

 

Steve, I originally used a Perkin Elmer system for filter measurement, but I lost my access to that in September 2017. I now use an Ocean Optics FX UV-VIS spectrometer, in combination with one of the OO DH-2000-BAL light sources. The SEU work was done with that.

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OK, then how does this idea sound, would you all like me to classify the U-360 1mm stack as a UV only filter?

 

It all depends on what we/you reads into the word "only"

This is something that would be good to discuss further.

 

Even a Baader U or a U-360/S8612 2mm+2mm-stack transmit ca 1% at 400nm.

 

The U-360/S8612, 1mm+2mm-stack transmit ca 8% at 400nm.

At 390nm it transmit 43% and at 410nm ca 0.4%

 

If OD4 or OD5 should be used as a decision level for "UV-only", there would just be UG11-stacks left.

 

None of these filters transmit anything significant further away from 400nm, for the normal UV-photography we are doing, regardless of if it is floral macro- or landscape-photography.

 

Functional-wise I would like to say they all belong in the UV-only group as images are completely dominated by the UV-light.

My reasoning behind that the decaying filter transmission slope at 400nm is steep enough to make that happen.

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I agree with Ulf's analysis. Functionally, the various filters discussed here are UV-only. Photos made with a U360/2+2, BaaderU, Seu2 all successfully capture UV signatures of whatever subject is being photographed.

 

I don't think any of these filters need classification as "UV-only". They have always been offered as "UV-pass" filters or dual-bandpass filters (when not IR-blocked). Buyers can look at transmission charts and make up their own minds about what OD they want.

 


 

I think I should try those 3 filters I just mentioned on the Monochrom now that I have learned it can shoot UV so well. I've ordered an adapter so that I can use the UV-Nikkor on the MM1. Perhaps seeing UV images made without the distraction of false colour would be useful to this discussion?? Jonathan also could try some experiments with his Mono cams to try to find actual evidence or not of viole.t

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As I said, "I leave it to others to define what a 'UV-only' filter is, should be, or what you want it to be".

However, for as long as I have been involved in this, a UV-only filter cuts off at 400nm.

The VV (visual violet) light may only change the blue color a little, but technically it is a mix of UV and visual light, not UV only.

So it is a little like saying UVIVF that is illuminated with unfiltered UV light is visual fluorescence only.

Of course usually any blue light emitted by the unfiltered torch only changes the results slightly, just like the UV+VV filters may only have slightly different color,

take a look at the difference in color between Ulf's comparisons here:

http://www.ultraviol...__fromsearch__1

 

He shows three stacks:

UG2A 2mm + S8612 2mm

UG1 1mm + S8612 2mm

UG1 2mm + S8612 2mm

These have progressively less VV mixed in with the UV, and you see a difference in the blue colors.

This is not unlike filtered and unfiltered UV light used to excite fluorescence.

It is a very similar scenario. If you want to ignore the facts because they don't matter, then that is your prerogative, I am only pointing out the facts.

Artistically, they are all nice to look at, but which one has more visual light mixed in to the UV photo?

If we thought that way about UVIVF then none of us would be filtering out torches.

Science and art both matter. We try to be accurate, clear and precise, and present the facts for people here.

 

"I don't think any of these filters need classification as "UV-only". They have always been offered as "UV-pass" filters or dual-bandpass filters (when not IR-blocked). Buyers can look at transmission charts and make up their own minds about what OD they want."

 

I think we do, and always have differentiated UV-only filters from UV+X+X filters.

Dual band is a whole other thing, and not what we are talking about here.

Once upon a time most people didn't accept the idea of a UV+Blue+Green range filter, such as the UG5/U330 + S8612 stacks.

What do we call those? UV pass filters? No, they are UV+Blue+Green pass filters, they are not classified as UV-pass filters.

"Buyers" may not understand what they are buying.

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The problem with mutually agreed upon scientific definitions is that that that biology does not always recognize them. While it is very useful for science to define a standard by declaring that 400 nm somehow separates ultraviolet radiation from visible in a continuous spectrum, try telling that to the human eye which can often see down to 370 nm. Indeed, visible violet is most often defined as those wavelengths in the interval between 380 - 450 nm. That is quite a lot more visible violet than has been discussed so far in this topic where everyone is quibbling over a mere 5 nanometers in the no-man's-land between 400 - 405 nm. If the standard definition of violet were applied, then all our commonly used broadband filters or stacks would need labeling as UV+Violet.
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400nm to 405nm is not mere. It makes a big difference in exposure time and color balance, and it may be a little more than just 5nm.

This is not about violet or the definition of violet. The point is about 400nm, which is the defining line between UV and visual as those are defined.

 

Wiki

Ultraviolet (UV) is electromagnetic radiation with a wavelength from 10nm to 400 nm, shorter than that of visible light but longer than X-rays

Ultraviolet A UVA 315–400

Near ultraviolet NUV 300–400

 

Violet is the color at the end of the visible spectrum of light between blue and the invisible ultraviolet. Violet color has a dominant wavelength of approximately 380-450 nanometers.

 

This is why I keep telling you that violet is a poor word to use in this context, because it crosses the line between UV and visual. You have insisted that I use that word,

so the only way to use that word in this context is to divide into two terms. UV Violet and Visible Violet.

I would just as soon call anything above 400nm 'blue', in the context of the BGR visible range.

The best term would just be 400nm+ or even just 'visual'.

The definition between UV-only and not is the 400nm line.

 

Enough said.

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I understand and respect your comments. (((Except for the part about wanting to call 'violet' as 'blue'. I get complaints about that. :lol: )))

 

I rather like the idea of letting violet be 400-450 nm and labeling the visible colour under 400nm as something like 'violet-uv', similar to a labeling such as 'yellow-green' or 'red-orange'.

 

But...... why is 400nm the divider? Some references give 390nm and some give 380nm.

 

It is interesting to look at a solar spectrum for UV and visual only because it spreads the chart out a bit so that more detail is available.

 

In the attached chart (from a reptile website) we can easily see the case for 400 nm as a divider because that is where the solar spectrum takes a giant leap for sol-kind. But that is a physics/astronomy approach. If we take a biological human-vision approach, then 380nm or 390nm makes more sense as a divider between UV and visual. If we were to take a hypothetical bee-centered approach, then there is no divider. :lol:

 

So any one of 380/390/400 as a defining divider is valid when taken in proper context.

 

I tend to place the UV/Vis divider lower at 380 or 390 nm because a significant number of the floral UV-signatures have something going on which shows up best around 350-360 nm.

 

 

I've been trying to find this chart without the lamp overlay.

spectrumExoTerraSolarGlo160W.gif

 

 

.

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I think we have strayed from any meaningful subject. We don't need or want, imo, marketing phrases like "UV-only" in order to make our purchasing decisions. The purpose of superlatives such as "pure" are intended to provide a cover for impurity. :) For example, if you are buying a goose down jacket, you probably assume that one that is labeled as "white goose down" is superior to a jacket that is sold as "90% goose down." You would be wrong. The clothing industry has received a deferment from truth on the words "goose down". By law "goose down" must only be 75% goose down, not 100% goose down, as the makers hope you will assume. The other 25% may be cheaper duck down, waterfowl feathers, landfowl feathers, etc.

 

Just so, the notion of "UV-only" is an attempt, not to aid the consumer, but to mislead the consumer. Why does the UV-photographer require such an ambiguous term when he/she has access to a transmission curve? What does "only" mean? By law, terms like "pure", "full", and "only" are seldom permitted in advertizing of critical products. This is because "pure", "full", and "only" are states that are difficult to attain and prove.

 

"Only" is an absolute condition, there are not degrees of "only". No commercial UV-bandpass filter available for less than $1000, has an instant drop at 401nm to OD5 and continues or exceeds OD5 to 1100nm. That, however, is what UV-only means to me and probably others. We don't require ambiguous marketing phrases to make our purchasing decisions if the filter dealer provides solid data from testing.

 

Just one opinion, YMMV

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  • 3 weeks later...

As promised, I re-visited my filter transmission measurements once my calibration standard for my spectrometer had arrived. It has and I have now recalibrated my spectrometer. As expected, it was out, slightly, but not by as much as I thought. Here are my two scans for the SEU II filter (before and after calibration of the spectrometer). Firstly from 280nm to 480nm.

post-148-0-32786200-1542808880.jpg

 

And from 395nm to 410nm, again before and after calibration.

post-148-0-41760800-1542808879.jpg

 

Finally here are the values from the calibration lamp. Two columns, first column the theoretical Hg peak positions for the lines, and second column the values from my spectrometer.

post-148-0-95438800-1542809001.jpg

 

I'm within +/-0.1nm in the region I'm interested in (330nm to 405nm) which is probably as good as I can expect from the device.

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